So I'm going to now do a second class of problems.

现在我要开始讨论另一类问题
We will return to this issue later.

我们过一会再回到这个问题
By the way, one thing I should mention to you.

我要顺便提醒你们一件事
Suppose the particle is not moving in a circle,

假设这个质点不是做圆周运动
but does this.

而是这样
Let's take a circle and just keep a quarter of the circle.

我们来画一个圆只画四分之一圆即可
During this part, when you're doing a quarter of a circle,

在这部分当你沿着四分之一圆运动
this is supposed to be a quarter of a circle.

这就是个一个圆的四分之一
You have the same acceleration directed towards the center.

同样是直接指向圆心的加速度
In other words,

也就是说
you don't have to be moving actually in a circle to have the acceleration.

你不必真的在一个圆上运动以获得相应的加速度
At any instant, your motion, if it follows any curve,

在任何时候如果做曲线运动